The present invention relates to a technical field of a seat belt retractor for winding up a seat belt while allowing winding and withdrawal of the seat belt. More particularly, the present invention relates to a technical field of a seat belt retractor provided with a seat belt load limiting mechanism (hereinafter, sometimes referred to as “EA mechanism”), which, by means of an energy absorbing member such as torsional deformation of a torsion bar, limits load acting on the seat belt to absorb energy added to an occupant when the seat belt is locked in the event of an emergency such as a vehicle collision where a large deceleration acts on the vehicle under the condition that the occupant wears the seat belt, and a seat belt apparatus having the same.
Conventionally, a seat belt apparatus installed in a vehicle such as an automobile restrains an occupant with a seat belt thereof in the event of the emergency as mentioned above. The seat belt apparatus comprises a seat belt retractor. In the seat belt retractor, the seat belt is wound onto a spool when the seat belt apparatus is not used and is withdrawn from the spool to be worn by the occupant when the seat belt apparatus is used. A locking mechanism of the seat belt retractor is actuated in the event of an emergency as mentioned above so as to prevent the spool from rotating in a belt withdrawing direction, thereby preventing the seat belt from being withdrawn. Accordingly, the seat belt restrains the occupant in the event of the emergency.
In the seat belt retractor of the conventional seat belt apparatus, the occupant is forced to move forward due to large inertia because a large deceleration acts on the vehicle when the seat belt restrains the occupant in the event of the emergency such as the vehicle collision. Accordingly, a large load is applied to the seat belt and the occupant receives a significant force from the seat belt. This force does not cause a serious problem to the occupant, but it is preferable to limit this force.
For limiting this force, a seat belt retractor has been proposed which is provided, in addition to a torsion bar, with a second EA mechanism which can operate independently so as to further flexibly and variously set the limited load applied on the seat belt according to information in the event of the emergency (for example, see Japanese Unexamined Patent Application Publication No. JP-A-2008-114659: Patent Document 1). According to the seat belt retractor disclosed in Patent Document 1, the limited load can be flexibly and variously set according to the situation in the event of the emergency. Therefore, it is possible to effectively and suitably restrain the occupant during the vehicle collision.
In the seat belt retractor disclosed in Patent Document 1, it is necessary to activate a gas generator for the second EA mechanism whenever the second EA mechanism is operated. Therefore, the second EA mechanism cannot be effectively operated.
The present invention has been made under the aforementioned circumstances and an object of the present invention is to provide a seat belt retractor wherein, in addition to a first EA mechanism, a second EA mechanism is independently and effectively operated so as to flexibly and variously set the limited load applied to the seat belt depending on the emergency situation, and a seat belt apparatus having the same.
Further objects and advantages of the invention will be apparent from the following description of the invention.